The present invention relates to pressure canisters and, more particularly, to an improved, lightweight pressure canister having a corrosion-resistant tube body that is magnetic pulse welded about a pair of distally disposed end caps.
The art of fabricating containers and vessels has its roots in antiquity. In modern times, containers and vessels of all types, shapes, and sizes are fabricated to meet the needs of a rapidly expanding world economy. The present invention relates to the manufacture of lightweight canisters capable of storing materials under a pressure of at least approximately 1,800 psi.
The typical method of fabricating pressure-type canisters is to weld a pair of distally placed closure elements, or end caps, to a metal shell body. However, lightweight aluminum canister tube bodies are not conducive to conventional welding. Heretofore, aluminum welding had to be performed in an expensive, inert atmosphere of argon to prevent an oxide coat from forming and interfering with the weld process. More importantly, aluminum tends to anneal and weaken when subjected to welding temperatures, thus necessitating a thicker shell body. The thicker shell adds weight and cost to the finished product and defeats the lightweight objective. The thicker tube shell has the obvious further disadvantage of reducing the amount of material that can be stored in the canister.
U.S. Pat. No. 5,979,694, issued to Bennett et al., discloses a lightweight aluminum canister that forms a mechanical seal with its end caps by electromagnetic forming. In electromagnetic forming, an electric coil is placed around a metal body, and is thereafter electrically pulsed to create a magnetic field that shapes the metal. In the aforementioned patent, coils are placed about the distal ends of the shell tube. The coil is then electrified with a high energy voltage pulse of short duration, which magnetically forms and mechanically seals the shell body about the end caps. A typical electromagnetic forming process is also described in U.S. Pat. No. 3,837,755, issued to Benoit et al. on Sep. 24, 1974, entitled MULTI-PIECE ROD FOR CONTROL AND STRUCTURAL MEMBERS; and U.S. Pat. No. 4,523,872, issued to Arena et al. on Jun. 18, 1985, entitled TORSION RESISTANT GROOVED JOINT.
The end caps used in the pressure canister of the Bennett et al. ""694 patent can be formed from a variety of metallic or non-metallic materials, preferably the end cap material being a plastic material. A suitable plastic that was chosen with the required attributes of light weight, strength, and ductility was Delrin(copyright), an injection moldable thermoplastic, fabricated from an acetal resin.
The present invention reflects the discovery that magnetic pulse welding can be used to hermetically seal end caps to the metal shell body. In this instance, higher internal pressures can be sustained over the aforementioned electromagnetically formed design, as the O-ring is eliminated. Tests have shown such pressure canisters to sustain internal pressures in excess of 1,800 psi without failure. Typically, the joint is stronger than the weakest material. Therefore, in an overpressure situation, the aluminum tube bursts away from the magnetic pulse welded joint while the joint itself remains intact. End caps are made of lightweight metal alloy materials, such as aluminum. The magnetic pulse welding process is similar to electromagnetic forming in that the joining technique occurs with an absence of heat. Thus, like the electromagnetic forming process, thinner material can be used in the inventive system for the cylindrical metal shell body, because no localized annealing of the metal occurs due to heating effects, as is common in conventional welding. Although the end caps can be made of most ferrous and non-ferrous metals, in the preferred embodiment the end caps are made of aluminum for weight and cost considerations.
It is an object of this invention to provide an improved pressurizable canister for storing and dispensing volatile materials under pressure.
It is a further object of this invention to provide a lightweight, metal, pressurizable canister that does not require conventional welding of the end caps, but uses instead a magnetic pulse welding technique.
In accordance with the present invention, there is provided a pressure vessel, or pressurizable canister. The canister comprises a hollow, thin-walled, cylindrical metal shell. The preferred metal is aluminum since light weight is a consideration for the vessel. Two metallic end caps are mechanically sealed to the respective distal ends of the metal shell tube by the process of magnetic pulse welding. The end caps are each cylindrically shaped, and have at least one circumferential recess to accommodate the metal of the shell tube as it deforms about the end caps. The tube shrinks into the recess of the end caps, and forms an intermolecular bond/weld between the tube and end cap. The top end cap may have an integrally formed mounting abutment that has a screw thread for attachment purposes. In this instance, a second recess is concentrically disposed in the facial surface of the top end cap in proximity to the mounting abutment.
In alternative design, a quick disconnect and pressure relief valve are combined in the same end-cap or alternatively one valve may be disposed in each cap. In yet another embodiment, multiple canisters can be connected to a manifold via pipe nipples and a single quick disconnect and pressure relief valve used in the manifold. No integrally formed mounting abutment and no face seal are required.